Derivatives of tetrahydrofuran



3,356,414 Patented Oct. 31, 1967 3,350 414 DERIVATIVES OFTliTRAHYDROFURAN Perry A. Argabright, Cranford, N.J., assignor to EssoResearch and Engineering Company, a corporation of Delaware No Drawing.Filed June 19, 1962, Ser. No. 203,655

17 Claims. (Cl. 260347.7)

thermal stability, and capability of imparting high specific impulseperformance to rocket propellant compositions.

The reactant furan is a commercially available .material. High purityfuran has a boiling point of close to 32C. under atmospheric pressure.It is regarded as having the following structure:

Furan is a S-member het rocyclic compound having oxygen as thehetero-ate and having conjugated double bonds. This arrangement istermed the furan nucleus.

Techniques found useful in interest may have one or more substituentgroups replacing hydrogen attached to the furan nucleus. Preferably, thesubstituent groups are organic functional groups that have a double bondconjugated with the double bond in the furan nucleus that containscarbon linked to nitrogen, oxygen, or both, that remain unchanged duringthe reaction of the substituted furan with N F In this regard, suitablefunctional groups are carbomethoxy, carbonyl halide, isocyanate,carboxy, carbonitrile, and carboxaldehyde groups. These substitutedfuran derivatives have differences in properties that impose the needfor certain modifications within the general principles hereindescribed.

The products that derivatives With N F uses.

Separate U.S. applications, Serial No. 77,462 and Serial No. 77,465,filed December 21, 1960, by Passannante et a1. and Michael et a1.pertain more specifically to the mono-functional and the bi-functionalfuran derivatives, respectively.

To form good yields of the difiuoramino derivatives of furan having atleast one NF group per C, precautions form by reaction of furan and itshave differences in properties and or prevent undesired polymerizationor tar formation.

A technique found useful in preventing tar formation during the reactionof furan with N F involves treating the reactor, particularly a glassreactor, with nitric acid followed by vacuum drying of the reactor atflame temperature. This prevents the presence of such basic whichpromote tar formation.

Another technique found useful for preventing tar formation 1n thereaction of furan and its derivatives with cold spot condensation ofintermediate reaction products on the Walls of the reactor leads to tarformation.

The reaction of furan and various derivatives thereof with N F can becarried out in the vapor, liquid, or mixed phase and in a static or flowsystem.

In general, the reaction of furan with N F proceeds satisfactorily at atemperature above C., preferably in the range of about C. to 450 C. Thereaction period or residence time, usually in the range of about 1 to 24hours, varies inversely to the temperature.

Lowering of the reaction temperature substantially below 135 C.,especially with increased pressure, has been indicated to lead to tarformation and unsatisfactory reaction.

Increasing the reaction temperature into the range of about C. to about450 C. makes the reaction of furan with N F even more selective towardthe formation of tetrakis (NF furan. Products containing even more furanreactant proportion of N F diluent, and temperature of reaction. Forexample, in using a glass reactor and a temperature in the range of 135to 185 C., with The N F is generally used in a proportion of at least 2mols per mol of the furan compound, i.e. at least stoichiometricproportion, for addition of may be increased to 10 to 1 or higher.

'With the principal aim of forming the desired high- 1 NF per C in thenucleus.

If a relatively small amount of the lower NF adduct product is formed,recovery of the higher adduct product is simplified and losses ofmaterials are decreased,

When practical requirements with N 13; to obtain products having ahigher NF content, e.g. tetrakis (N1 furan.

One suitable product separation method employs concentrated sulfuricacid for extraction of the lower adducts having an unreacted double bondin the furan nucleus. This method works well at ambient or lowertemperatures in the range of to 30 C. without causing tar formation orreaction that would prevent or impair recovery of the desired productsin which the furan nucleus is entirely saturated by addition of at least4 NF groups per carbon in the nucleus. The following examples are givenon the synthesis and isolation of the desired furan derivatives havinghigh NF content.

Example 1 In a typical experiment, 5 millimoles furan were reacted with11 millimoles N F at 145 C. for 18 hours. The reaction was carried outin a glass bulb reactor (treated with HNO prior to reaction) at astarting pressure of 620 mm. Hg. The colorless product weighed 740 mg.By nitrogen and fluorine analysis, the mixture was shown to contain 37%by weight of the diadduct (tetrakis (N1 furan). The remainder of theproduct is the monoadduct (bis (NF furan). The mixture was extractedwith concentrated H 80 at room temperature (ca. 21 C.) until the H 80layer was no longer colored. The organic layer was distilled in vacuo atroom temperature to free it from any dissolved H 80 Analysis: 54.3percent F, (theory for diadduct 55.1); 20.0 percent N (theory fordiadduct 20.3); (1 1.604; n 1.3830; v (23 C.), 1 mm.

The infrared spectrum of this purified product was in agreement with theN H diadduct structure.

Through the addition of 2 moles of N F to the furan, the resultingdiadduct structure is obtained:

The diadduct thus formed from furan has a high ratio of NF per molecule.This compound is tetrakis (N1 furan. The vapor pressure of the diadductis satisfactorily low compared to other kinds of tetrakis compounds. Bymaking the tetrakis (N1 furan derivative containing 1 NF per C, theproduct formed has a relatively high density which is favorable for apropellant of high relative boost velocity. Thedifluoraminotetrahydrofuran product has suitable stability for storage.It may be used as an oxidizer in both solid, liquid, and hybridhighenergy propellant systems.

The tetrakis (N1 adduct of furan has been found to have an extremelyhigh thermal stability compared to other NF -containing compounds. In a90 C. storage test, no decomposition was observed from the tetrakis (NFfuran adduct for over 1000 hours.

Example 2 Using as feed a reaction product obtained, as in Exa-mple 1,under low pressure, said product containing 20% of the tetrakis (NFfuran adduct and 80% of lower adducts, this feed with twice the volumeof carbon tetrachloride was heated for one hour at 150 C. with enoughadded N F to maintain a pressure of about 450 psi. in a stainless steelautoclave (previously treated with HNO The resulting crude product wascooled, treated with H 80 at room temperature, and the undissolvedorganic portion recovered was the desired tetrakis (N1 furan adduct. Itamounted to 70% of crude product.

The two-stage operation in Example 2 demonstrated a method of increasingthe yield of tetrakis (NF product, and also of shortening the overallreaction period.

A suitable feed may also be derived from a flow reactor wherein agaseous mixture of N 1 and furan is allowed to react at temperaturesranging from 150 to 300 C. at contact times of from 30 seconds to 10minutes. The gaseous products (his and tetrakis (N1 furan) are removedby condensation and the unreacted N F and furan recycled for furtherreaction. The reactor is a tube composed of an inert material, such asstainless steel, and heated by a strip heater provided with temperaturecontrollers.

Example 3 To 2.63 millimoles of bis (N1 furan adduct mixed with 1.5milliliters of CCl.; diluent was added 5.72 millimoles of N 1 in a 5 ml.capacity stainless steel autoclave (pretreated as above). The reactionmixture was heated to 150 C. under a pressure of about 450 p.s.i.a. for15 hours. The amount of N F reacted was 1.3 millimoles per mole of thehis adduct. The resulting product mixture obtained thus includedtetrakis (N1 adduct and some higher NF content products presumablypentakis (N1 and hexakis (N1 furan.

Example 4 To determine relationship of yield and product composition toreaction temperature, comparative tests were made on adding N 13; tofuran under a pressure of 700 mm. Hg absolute. A 2 to 1 mole ratio of NF to furan was used. The results are summarized as follows:

TABLE I Product Percent Percent Temp, C. Time, Hrs. Yield, TetrakisLower percent Adducts The data summarized under Table I shows thathigher temperatures are more effective in forming the furan derivativesof higher NF content selectivity. At C. and lower temperatures, thereaction of N F with furan tends to produce lower adducts and tar (dueto extensive reaction times).

The furans containing at least 1 N1 group per C in the furan nucleus areuseful sought-after ingredients for rocket propellants. They greatlyincrease the thrust power per unit weight as measured by specificimpulse, lsp. They are useful in plastisol and solid composites whichcontain a binder. For example, in a propellant containing 0.85% boronpowder, 13.65% hydrazinium nitroformate, and 20% nitro rubber binder,65.5% of tetrakis (NF furan adduct gives the product a specific impulseof 277 seconds. By using the pentakis (N1 furan derivative in a similarcomposition with a small increase in percentage of the boron, the lsp isincreased to 288.

It is not intended to limit the invention to the examples whichdemonstrate embodiments of the invention claimed. The invention claimedis intended to include all inherent novelty, modifications andequivalents coming within the scope and spirit of the invention.

What is claimed is:

1. Difluoramino adduct of furan having an NF group attached to each of 2to 4 carbon atoms in a furan nucleus.

2. Bis (N1 adduct of furan.

3. Tetrakis (N1 tetrahydrofuran.

4. A mixture of his (NF and tetrakis (NF adducts of furan.

5. Process for preparing his (NF adduct and tetrakis (NF adduct of furanwhich comprises reacting furan with N F at a temperature of about to 450C., and recovering resulting adduct product.

6. Process as defined in claim 5, wherein the N 13; is reacted with thefuran in a vapor phase reaction mixture.

7. Process as defined in claim 5, wherein the resulting adduct productis condensed to a liquid, substances in the resulting liquid productwhich are soluble in concentrated H 80 at low temperatures areextracted, and the tetrakis (NF adduct of furan which is insoluble inthe H 80 is vacuum distilled to recover it as a separate product.

8. Process of forming tetrakis (NF tetrahydrofuran, which comprisesadmixing N F with furan in a ratio to reaction mixture, maintaining saidreaction mixture at a reaction temperature in the range of about 135 to450 C. for a period until tetrakis (NF tetrahydrofuran is formed byreaction of the N F with the furan.

9. In the process of claim 8, maintaining the reaction mixture under apressure in the range of 5 to 3000 p.s.i.a.

10. In the process of claim 8, carrying out reaction of the N F with thefuran in contact with glass reactor wall surface that is previouslytreated with nitric acid and then dried.

11. In the process of claim 8, carrying out reaction of the N F with thefuran in said reaction mixture with an inert diluent present in themixture.

12. Process of preparing difluoramino furan derivatives containing 4 NFgroups attached to carbon atoms in the furan nucleus, which comprisesreacting furan with N F at a moderate reaction temperature in the rangeof about 100 to 185 C. to add 2 NF groups to the furan nucleus, thenreacting a resulting bis (N1 adduct of the furan with N F underincreased pressure above atmospheric pressure to link 2 more NF groupsto carbon atoms in the furan nucleus of the his (NF adduct.

13. Process of preparing furan derivatives containing 4 NF groupsattached to 4 carbon atoms in the furan nucleus, which comprisesreacting bis (NF adduct of furan with N F under superatmosphericpressure to attach 2 more NF groups to carbon atoms in the furannucleus.

14. The process as defined in claim 13 in which the his (NF adduct isreacted with N F in the presence of 15. Process of preparing tetrakis(NF adduct of furan, which comprises reacting furan in vapor phase WithN F in a proportion to add an NF group to each of 2 carbon atoms in thering nucleus of the furan at a temperature in the range of to C., thenreacting the resulting product containing his (NI- adduct of furan withmore N F at a temperature in the range of 135 to C. undersuperatmospheric pressure to form tetrakis (diiluoramino)tetrahydrofuran from said his adduct, and recovering the tetrakis(difiuoramino) tetrahydrofuran.

16. In the process as defined in claim 15, reacting the bis (NF adductwith the N F in the presence of CCL; as inert diluent.

17. Process for reacting N F with furan to saturate both double bonds ofthe furan nucleus in a single stage at a rapid rate which comprisesadmixing at least about 2 moles of N F with each mole of furan, andheating the mixture to a reaction temperature of 225 to 450 C.

under a pressure of about 5 to 14.5 p.s.i.a., for a period of betweenabout 0.1 to 1 hour, and recovering the resulting product rich intetrakis (difluoramino) adduct of furan and higher nitrogen andfluorine-containing NF adduct product of the furan.

References Cited UNITED STATES PATENTS 3,215,709 11/1965 Logothetis260349 OTHER REFERENCES Hoffman et al., Chem. Reviews, vol. 62, pp. 1 to18 (1962).

NICHOLAS S. RIZZO, Primary Examiner. L. D. ROSDOL, Examiner.

J. W. WHISLER, Assistant Examiner.

1. DIFLUORAMINO ADDUCT OF FURAN HAVIN G AN NF2 GROUP ATTACHED TO EACH OF2 TO 4 CARBON ATOMS IN A FURAN NUCLEUS.